Add multi-site Caddy helpers and document usage

- add startup/shutdown scripts that render a Caddyfile from JSON config and run health checks

- add Python utilities and a sample sites.json for declarative multi-site configuration

- document the workflow and ignore generated Caddy state artifacts

- normalize double-quote style across challenge workflow controllers, nodes, and tests

docker/shutdown-caddy.sh

@@ -0,0 +1,49 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+STATE_DIR="$SCRIPT_DIR/caddy/state"
+PID_FILE="$STATE_DIR/pids/caddy.pid"
+STARTUP_LOG="$STATE_DIR/logs/startup.log"
+SHUTDOWN_LOG="$STATE_DIR/logs/shutdown.log"
+
+mkdir -p "$(dirname "$PID_FILE")" "$(dirname "$SHUTDOWN_LOG")"
+
+log() {
+    echo "$(date '+%Y-%m-%d %H:%M:%S') [INFO] $1" | tee -a "$SHUTDOWN_LOG"
+}
+
+error() {
+    echo "$(date '+%Y-%m-%d %H:%M:%S') [ERROR] $1" | tee -a "$SHUTDOWN_LOG" >&2
+}
+
+if [ ! -f "$PID_FILE" ]; then
+    log "No Caddy PID file found; nothing to stop."
+    exit 0
+fi
+
+PID="$(cat "$PID_FILE")"
+if ! kill -0 "$PID" >/dev/null 2>&1; then
+    log "Caddy process (PID $PID) not running; removing stale PID file."
+    rm -f "$PID_FILE"
+    exit 0
+fi
+
+log "Stopping Caddy (PID $PID)..."
+if caddy stop --pidfile "$PID_FILE" >/dev/null 2>&1; then
+    log "Caddy stopped successfully."
+    rm -f "$PID_FILE"
+else
+    error "Failed to stop Caddy via caddy stop; attempting manual kill."
+    kill "$PID" >/dev/null 2>&1 || true
+    sleep 2
+    if kill -0 "$PID" >/dev/null 2>&1; then
+        error "Unable to stop Caddy (PID $PID)."
+        exit 1
+    fi
+    log "Caddy process terminated."
+    rm -f "$PID_FILE"
+fi
+
+log "Shutdown complete. Logs available at $STARTUP_LOG and $SHUTDOWN_LOG."